1. Field of the Invention
The present invention relates to a fixed wireless access system, and more particularly to a P-MP (point-to-multipoint communication) system using frequencies of quasi-millimeter and millimeter wave bands, configurations of base and subscriber stations constituting the P-MP system, and a method of use thereof.
2. Description of the Related Art
In a fixed wireless access system for radio communication between a base station installed by a telecommunications carrier and a subscriber station at each user""s premises (refer to Nikkei Communication issued Sep. 6, 1999, pp. 106 to 112, for example), a wide frequency range is available in quasi-millimeter and millimeter wave bands. The fixed wireless access system is therefore expected to provide high-speed access lines at low charge. In particular, a conventional P-MP system, which is a type of fixed wireless access system (refer to ARIB, Association of Radio Industries and Businesses, STD-T59 Issue 1.0), is designed for connecting a base station and tens to hundreds of subscriber stations on a point-to-multipoint basis with the intention of providing services to SOHOs (small offices/home offices) and individual users. For implementation of the P-MP fixed wireless access system using quasi-millimeter and millimeter wave bands, it is required to ensure a line-of-sight communication path between the base station and each subscriber station. As a technique for ensuring line-of-sight communication, an antenna may be installed at an elevated position or a repeater may be used. However, because of a substantial increase in cost, the installation of an antenna at an elevated position or the use of a repeater is economically disadvantageous. For a wireless telephone system bearing a close resemblance to the above situation, a wireless telephone apparatus having a repeating function is disclosed as a low-cost repeating facility in Japanese Unexamined Patent Publication No. H11 (1999)-243362.
With reference to FIG. 1, the wireless telephone apparatus having a repeating function is described below. As shown in FIG. 1, a wireless telephone apparatus 90 comprises a first radio circuit 91 including a first receiver 95 and a second transmitter 96, and a second radio circuit 92 including a second receiver 97 and a first transmitter 98. For employing the wireless telephone apparatus 90 as telephone equipment for direct communication with a base station, the first radio circuit is made active. For employing the wireless telephone apparatus 90 as wireless telephone repeating equipment, the wireless telephone apparatus 90 is located at a place suitable for relaying communication and then a repeating function start switch thereof (not shown) is turned on. In the latter case, the first receiver 95 and the first transmitter 98 are used for relaying radio signals from the base station to a different wireless telephone apparatus, and the second receiver 97 and the second transmitter 96 are used for relaying radio signals from the different wireless telephone apparatus to the base station. For employing the wireless telephone apparatus 90 as wireless telephone equipment for communication with another wireless telephone apparatus serving as a repeater, the second radio circuit 92 is used.
In the conventional P-MP fixed wireless access system using quasi-millimeter and millimeter wave bands, wherein such a wireless telephone apparatus having a repeating function as mentioned above is employed as a subscriber station for the purpose of providing an additional feature, the following disadvantages are involved:
(1) No means for judging whether or not to use the repeating function is disclosed. It is therefore required to perform a manual operation, causing inefficient communication.
(2) An RF module for use in quasi-millimeter and millimeter wave bands comprises an MMIC (monolithic microwave integrated circuit), which is still high-priced. In addition, a plurality of transmitter-receiver radio circuits for relaying signals in transmission and reception must be provided in a subscriber station, resulting in an increase in cost.
(3) In the ARIB STD-T59 Issue 1.0, the use of a directional antenna at a subscriber station is specified as a mandatory requirement. However, no means for forming a judgment on orientation of the antenna is disclosed, and there arises inefficiency in communication where a manual operation is necessary.
It is therefore a principal object of the present invention to provide a fixed wireless access system including a base station and a plurality of subscriber stations, each having a repeating function, wherein the subscriber station judges whether or not to repeat signals without user""s intervention, and if it is judged that signal repetition is needed, an optimum relaying path and an optimum antenna are selected automatically, i.e., autonomous routing is set up.
Another object of the present invention is to provide a simple type of transmitter-receiver radio circuit for each subscriber station while achieving the above principal object.
In accomplishing these objects of the present invention and according to one aspect thereof, there is a fixed wireless access system in which a plurality of subscriber stations carry out communication via a base station and at least one of the subscriber stations has a repeating function for relaying signals between a different subscriber station and the base station, the fixed wireless access system comprising: an arrangement wherein the subscriber station having the repeating function judges whether or not to repeat signals, and if it is judged that signal repetition is needed, the subscriber station finds out an optimum relaying path and records the optimum relaying path while registering the same in an upper-level subscriber station; and an arrangement wherein, in order to perform signal communication with an arbitrary subscriber station registered in the base station, the base station holds routing information which is used for determining whether or not to set up a relaying path via a different subscriber station registered in the base station, and according to the routing information, the base station allocates control and communication channels to the subscriber station for signal communication therewith.
The subscriber station having the repeating function comprises a buffer memory for temporarily storing signals to be communicated between the different subscriber station and the base station, and a first table for registering at least information for identifying a relaying path between an own reference wireless station thereof and a lower-level subscriber station for signal repetition via the subscriber station.
According to a preferred embodiment of the present invention, there is provided a P-MP fixed wireless access system based on a time-division multiple-access scheme in which the subscriber station having the repeating function comprises: a radio circuit capable of transmitting and receiving signals at the same frequency; a communication controller for identifying an incoming signal, for generating an outgoing signal, and for managing radio channels and an antenna to be used for transmission and reception; a timing controller for extracting a clock signal from the incoming signal to provide system synchronization; a receiving quality monitor for measuring reception quality of the incoming signal; an antenna selector for selecting an antenna to be used according to a selection signal issued from the communication controller; a plurality of directional antennas having respective directivities to different orientations; a buffer memory for temporarily storing signals to be communicated between the different subscriber station and the base station; a first table for registering information on a wireless station which serves as a clock supplier for the subscriber station when each of the plural directional antennas is used and for registering information for identifying a relaying path to a lower-level subscriber station for signal repetition via the subscriber station; a third table for recording a frame format; a first timer for indicating the upper limit of a period of searching for a wireless station serving as a clock supplier; a second timer for indicating the upper limit of a period of searching for a lower-level subscriber station to be connected with the subscriber station; and an interface controller for controlling input from and output to external input/output equipment.
Further, the base station comprises a radio circuit capable of transmitting and receiving signals at the same frequency; a communication controller for identifying an incoming signal, for generating an outgoing signal, and for managing radio channels; an antenna; a fourth table for recording a frame format for identifying each channel position and for recording a use status of each channel; an interface controller for controlling input from and output to external input/output equipment; and a second table in which information on each subscriber station is registered and in which, in order to perform signal communication with an arbitrary subscriber station registered in the base station, routing information is registered for determining whether or not to set up a relaying path via a different subscriber station registered in the base station.
In the present invention, the subscriber station having the repeating function may be a mobile telephone set or a stationary radio transmitter-receiver apparatus.
According to the present invention, in a fixed wireless access system in which a base station and a plurality of subscriber stations are provided with a radio circuit capable of transmitting and receiving signals at the same frequency, it is possible to implement a repeating function of each subscriber station in such a fashion that a judgment on whether or not to repeat signals is automatically formed using information regarding a condition of each subscriber station. Further, automatic re-routing can be performed in communication between the base station and an arbitrary subscriber station. The present invention is also applicable to a system including a plurality of subscriber stations each having a directional antenna. Therefore, since the repeating function of the subscriber station can be used readily, it is easy to expand a service area, contributing to a reduction in base station installation cost. Furthermore, according to the present invention, it is possible to readily cope with a failure in any subscriber station to be used as a repeater, and a new subscriber station can be installed with ease. Still further, since a subscriber station serving as a key relay point can be identified by the base station, differentiation in charging is implementable in an efficient fashion.
Still other feature and advantages of the present invention will become apparent to those of ordinary skilled in the art upon reading and understanding the following detailed description in conjunction with the accompanying drawings.